Semiconductor device fabrication typically involves extensive use of patterned etching of both semiconductor and dielectric materials. In particular, the formation of patterns of openings in silicon dioxide dielectric layers of silicon devices is widely used because of the passivating and optical effects of silicon dioxide on silicon surfaces. Patterned etching of silicon dioxide layers can be used to facilitate localised diffusions and metal contacts to underlying silicon, or in other cases, to provide a mask for etching the underlying silicon. Typically, the patterned etching of dielectric layers, such as silicon dioxide, has been achieved using photolithography or scribing.
However, photolithography requires costly equipment (e.g., mask aligners, mask writers), clean room environments, and generally many time-consuming steps. Changes in patterns require new mask sets. A typical photolithographic process for the formation of a pattern of openings in a dielectric typically requires deposition of a resist layer over the dielectric layer (usually by spin-coating), appropriately aligning a prepared mask over the resist layer, exposing the resist through the mask to UV radiation and then developing the exposed resist to form a pattern of openings in the resist. The resist with a pattern of openings is then used as a mask against etchants in wet etching and physical etching (e.g. ion etching) applications. Etching fluids for silicon dioxide typically comprise aqueous hydrogen fluoride or a buffered oxide etching solution, both of which are highly corrosive. The device is then rinsed to remove traces of the etchant, and finally the resist layer is removed to leave a patterned dielectric layer on the device.
More recently, inkjet methods of patterning a resist layer have been described. These methods remove the need to use photolithography for the patterning step, using instead an inkjet device to deposit a solution, which either creates openings or permeable regions in the resist layer, at predetermined locations. The thus-patterned resist layer can then be used to mask the underlying dielectric layer while the printed pattern provides a path for the etching of the dielectric during immersion in an etching solution. These inkjet methods of patterning a resist provide a potential low cost alternative to photolithography. Changes in the etching pattern can be realised quickly by changes in a digital image pattern used by the inkjet printer. However, like the photolithographic methods, they still involve many time-consuming steps and require the use of large quantities of chemicals, in particular resins for resist and corrosive etching solutions. Because of the need to use large quantities of corrosive solutions for the wet etching step, significant safety controls must also be adhered to in production environments. Therefore, advances which can reduce the number of processing steps and/or the amount of expensive and corrosive chemicals used in the patterning step are desirable. Furthermore, advances which minimise the risks to human operators when performing etching processes and reduce the amount of hazardous waste are also desirable.
In this specification, where concentrations are given as a percentage (%) this is intended to indicate a ratio of weights (w/w) unless otherwise indicated.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.